"It was [H.G. Wells'] adolescent fiction, his imaginative stories, that live forever - and yet are not acknowledged in literature classes as being great literature. So to hell with the academics!"
- Greg Bear

The exoskeleton fighting suit is, of course, a popular item of technovelgy. I think the first reference I can find is in Starship Troopers, by Robert Heinlein (see powered suit).

The Lieutenant Colonel was extremely dead. He'd come down from the heavens in his full NAFTA military power-armor, a leaping, brick-busting, lightning-spewing exoskeleton, all acronyms and input jacks. It was powerful, elaborate gear, of an entirely different order than the gooey and fibrous street tech of the two urban intrusion freaks.

But the high-impact crash had not been kind to the armored suit. It had been crueler still to the bone, blood, and tendon housed inside.

Of course, an exoskeleton can only do so much. Exoskeleton just means that the skeleton, the bony support for the soft parts of the body, is on the outside, where it can do double duty as armor (as well as support).

See the longer discussion for polycarbon exo, from Mona Lisa Overdrive, by William Gibson.

Take a look at this very nicely done anime treatment of exoskeletons. Be warned - you'll want to go fire up your exo right after watching it.